This invention relates to the preparation of semiconductor device structures. Particularly, the present invention pertains to dielectric films and methods of forming dielectric films, such as barium-strontium-titanate films.
Various dielectric films have been formed in the past during the fabrication of semiconductor devices. For example, films such as silicon dioxide and silicon nitride have been used for dielectric films in the formation of capacitors, such as for memory devices, including, for example, dynamic random access memories (DRAMs).
With the shrinkage of minimum feature sizes of semiconductor devices, the requirement of providing high capacitance with thinner films is becoming apparent. As the dielectric constant of silicon dioxide and silicon nitride are relatively low, the need for utilizing higher dielectric constant films, such as tantalum pentoxide and barium strontium titanate arises. Such high dielectric constant films provide the ability to achieve a larger capacitance value in a smaller area, e.g., with a thinner dielectric film. In other words, as memory devices become more dense, it is necessary to decrease the size of circuit components forming such devices. One way to retain storage capacity of storage cell capacitors of the memory devices and at the same time decrease the"" memory device size is to increase the dielectric constant of the dielectric layer of the storage cell capacitor. Additionally, as high density packing of devices increases, development of thinner dielectric films with a high dielectric constant and good physical and electrical properties is desired.
Ferroelectric thin films, such as barium-strontium-titanates (BST), for example, deposited on semiconductor wafers have recently gained interest for use in memory devices. Generally, these materials have high dielectric constants. However, the dielectric properties of such films are dependent on various film characteristics such as thickness. For example, the dielectric properties of conventional BST thin films are undesirably affected as the thickness of such films is decreased, e.g., decreasing dielectric constant with decreasing thickness. Such dielectric response of BST is described in the article, entitled xe2x80x9cThe dielectric response as a function of temperature and film thickness of fiber-textured (Ba,Sr)TiO3 thin films grown by chemical vapor deposition,xe2x80x9d J.Appl.Phys. 82 (5), Sep. 1, 1997; see also, Basceri, C., Electrical and Dielectrical Properties of (Ba,Sr)TiO3 Thin Film Capacitors for Ultra-High Density Dynamic Random Access Memories, (Ph.D. dissertation, 1997).
The present invention addresses thickness dependence of dielectric properties of dielectric constant materials, for example, such as high dielectric BST films. Methods for forming effective dielectric films, methods of forming structures incorporating such layers, e.g., the use of a thin dielectric film in a capacitor, and other methods associated therewith and structures formed thereby are described herein.
A method for use in fabrication of integrated circuits according to the present invention includes providing a substrate assembly having a surface and forming a barium-strontium-titanate film on at least a portion of the surface. The barium-strontium-titanate film includes an interfacial layer having an atomic percent of titanium less than or equal to the atomic percent of titanium in a bulk layer of the film.
In various embodiments of the method, the bulk layer of the barium-strontium-titanate film may include from about 50.0 atomic percent to about 53.5 atomic percent titanium, the interfacial layer may include from about 1 atomic percent to about 3 atomic percent titanium less that the bulk layer, the barium-strontium-titanate film may be less than about 600 xc3x85, and/or the interfacial layer may include a greater atomic percent of barium relative to the atomic percent of strontium.
In another embodiment of the method, forming the barium-strontium-titanate film may include decreasing a flow rate of a titanium-containing organometallic precursor to a deposition chamber during a first predetermined time period for forming the interfacial layer relative to the flow rate of the titanium-containing organometallic precursor during a predetermined time period for forming the bulk layer.
In another embodiment the method, forming the barium-strontium-titanate film may include increasing the total flow rate of a barium-containing organometallic precursor and a strontium-containing organometallic precursor to a deposition chamber during a first predetermined time period for forming the interfacial layer relative to the total flow rate of the barium-containing organometallic precursor and the strontium-containing organometallic precursor during a predetermined time period for forming the bulk layer.
In another embodiment of the method, the interfacial layer is formed in less than about 50 seconds after initially providing the organometallic precursors to the chemical vapor deposition chamber.
A method for use in formation of a capacitor according to the present invention is also provided. The method includes providing a first electrode having a surface and forming a barium-strontium-titanate dielectric film on at least a portion of the surface of the first electrode. The barium-strontium-titanate film includes an interfacial barium-strontium-titanate layer on at least a portion of the surface of the first electrode and a bulk barium-strontium-titanate layer comprising from about 50 atomic percent to about 53.5 atomic percent titanium. The interfacial layer includes about 1 atomic percent to about 3 atomic percent less titanium that the bulk dielectric film. A second electrode is then formed on at least a portion of the barium-strontium-titanate dielectric film.
In one embodiment of the method, the interfacial layer has a thickness of less than half of a total thickness of the dielectric film.
A method of forming a titanium-containing dielectric film according to the present invention includes forming a titanium-containing interfacial dielectric layer on a substrate assembly surface and forming a titanium-containing bulk dielectric layer thereon. The atomic percent titanium in the interfacial layer is less than or equal to the atomic percent of titanium in the bulk layer.
In various embodiments of the method, the dielectric film may include a material selected from the group consisting of BaSrTiO3; BaTiO3; SrTiO3; PbTiO3; Pb(Zr,Ti)O3; (Pb,La)(Zr,Ti)O3; (Pb,La)TiO3; and a combination thereof. Preferably, the dielectric film includes a BaSrTiO3 film and the interfacial dielectric layer comprises from about 1 atomic percent to about 3 atomic percent less titanium than the bulk dielectric layer.
In another embodiment of the method, forming the titanium-containing interfacial layer includes providing a first organometallic precursor and a titanium-containing organometallic precursor to a chemical vapor deposition chamber containing the substrate assembly. The concentration of the first organometallic precursor and the titanium-containing organometallic precursor in the chemical vapor deposition chamber is such that an equal or higher dielectric constant is attained for the interfacial layer relative to the bulk layer.
Yet further, another method of providing a dielectric film according to the present invention is described. The method includes forming a dielectric film using one or more organometallic precursors by forming an interfacial dielectric layer on a substrate assembly surface using the one or more organometallic precursors and forming a bulk dielectric layer on the interfacial dielectric layer. The atomic percent of at least one metal component present in the interfacial layer is controlled such that an equal or higher dielectric constant is attained for the interfacial dielectric layer relative to the bulk dielectric layer.
In one embodiment of the method, the atomic percent of at least one metal present in the interfacial layer is controlled by controlling a flow rate of at least one of the one or more organometallic precursors to a chemical vapor deposition chamber.
In another embodiment of the method, the interfacial layer is formed in an early nucleation stage after initially providing the one or more organometallic precursors to a chemical vapor deposition chamber. Preferably, the interfacial layer is formed in less than about 50 seconds after initially providing the one or more organometallic precursors to the chemical vapor deposition chamber.
A capacitor structure according to the present invention includes a first conductive electrode and a titanium-containing dielectric film formed thereon. The titanium-containing dielectric film formed thereon includes an interfacial layer formed on at least a portion of the first conductive electrode and a bulk layer formed on the interfacial layer. An amount of titanium in the interfacial layer is less than or equal to an amount of titanium in the bulk layer. Further, the capacitor structure includes a second conductive electrode formed on at least a portion of the titanium-containing dielectric film.
In various embodiments of the capacitor structure, the amount of titanium in the interfacial layer may be less than about 53.5 atomic percent, the titanium-containing dielectric film may be less than about 600 xc3x85 thick, the interfacial layer may include a greater atomic percent of barium relative to the atomic percent of strontium, and/or the interfacial layer may include a thickness of less than half of a total thickness of the dielectric film.
A dielectric film according to the present invention is also described. The dielectric film includes a titanium-containing interfacial layer and a titanium-containing bulk layer formed on the interfacial layer. The interfacial layer includes from about 1 atomic percent to about 3 atomic percent less titanium than the bulk layer.
Further, another capacitor structure is provided. The capacitor structure includes a first electrode and a barium-strontium-titanate dielectric film formed on at least a portion of the first electrode. The dielectric film includes an interfacial layer and a bulk layer such that the interfacial layer is in contact with the first electrode. An amount of titanium in the interfacial layer is less than or equal to an amount of titanium in the bulk layer. Further, the capacitor structure includes a second electrode formed on at least a portion of the bulk layer of the dielectric film.
In various embodiments of the structure, the bulk layer of the barium-strontium-titanate dielectric film includes from about 50.0 atomic percent to about 53.5 atomic percent titanium, the amount of titanium in the interfacial layer is about 1 atomic percent to about 3 atomic percent less than the bulk layer, the interfacial layer includes a greater atomic percent of barium relative to an atomic percent of strontium, and/or the interfacial layer is less than half of a total thickness of the barium-strontium-titanate dielectric film.
These and other objects, features and advantages of the present invention, e.g., use of the capacitor structure in a memory cell, will be apparent from the following description of various embodiments and as illustrated in the accompanying figures.